icauhtli.

Headword: 
icauhtli.
Principal English Translation: 

younger brother, cousin

Orthographic Variants: 
-ycauh , -yccauh , -iccauh , -teicauh , -teycauh
Alonso de Molina: 

icauhtli. hermano menor.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 32r. col. 1. Thanks to Joe Campbell for providing the transcription.

Lockhart’s Nahuatl as Written: 

iccāuh(tli). pl. possessed form -iccāhuan, because the uh of the stem was originally the possessive suffix. also seen as -tēiccāuh. (219)
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 219.

Attestations from sources in English: 

Amicuhtzin yquichcapa amechmotlapalhuia = Your younger brother salutes you from here (Mexico City, 1598)
Beyond the Codices, eds. Arthur J.O. Anderson, Frances Berdan, and James Lockhart (Los Angeles: UCLA Latin American Center, 1976), Doc. 33, 204–205.

yz ca yteycauh y nochhuetli ytonca tençozonmoc ha° mocuatequia = Here is Nochhuetl's younger sibling, named Teçoçomoc, not baptized.
(Cuernavaca region, ca. 1540s)
The Book of Tributes: Early Sixteenth-Century Nahuatl Censuses from Morelos, ed. and transl. S. L. Cline, (Los Angeles: UCLA Latin American Center Publications, 1993), 128–129.

iccauh = younger sibling or cousin of a male
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 219.

-teicauh = also seen for younger brother in some places.

Attestations from sources in Spanish: 

ynoteycauh Lurenzo Tamatlaneuh quimopilliz = mi hermano menor Lorenso Tomatlanehu, la ha de tener (Ocotelulco, 1593)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 1, Testamentos en castellano del siglo XVI y en náhuatl y castellano de Ocotelulco de los siglos XVI y XVII, eds. Teresa Rojas Rabiela, Elsa Leticia Rea López, y Constantino Medina Lima (Mexico: CIESAS, 1999), 234-235.

ynoteicauh Laurenço = mi hermano menor Lorenso Tomatlanehu, la ha de tener (Ocotelulco, 1593)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 1, Testamentos en castellano del siglo XVI y en náhuatl y castellano de Ocotelulco de los siglos XVI y XVII, eds. Teresa Rojas Rabiela, Elsa Leticia Rea López, y Constantino Medina Lima (Mexico: CIESAS, 1999), 234-235.

themes: 
Family, Kinship, Descent